Fin array for heat transfer assemblies and method of making same

ABSTRACT

A fin array for a heat exchanger and method of forming same are disclosed. The fin array is an elongated one piece element that includes a plurality of fins. The fins include connected staggered top segments and bottom segments. A top bend axis extends continuously across a plurality of the top segments.

RELATED APPLICATIONS

The present patent document is a continuation of PCT Application SerialNo. PCT/US03/20653, filed Jun. 30, 2003, designating the United Statesand published in English, which claims the benefit of the filing dateunder 35 U.S.C. § 119(e) of Provisional U.S. Patent Application Ser. No.60/392,075, filed Jun. 28, 2002, both of which are hereby incorporatedby reference.

BACKGROUND

The present invention relates generally to the field of heat exchangerassemblies. More specifically, the present invention relates to animproved design and method of manufacturing a fin array for use in aheat transfer assembly.

Fin arrays have been previously produced using a louvered design. Thelouvered fin array is folded in a serpentine pattern to form a series ofalternating rounded upper and lower crests with a plurality ofindividual fins. Each of the individual fins may include a plurality oflouvers. This fin array is manufactured from strips of metal, such ascopper or aluminum, that are driven through rotary cutting dies that cutthe openings in the strip and shape the louvers by pushing them inwardor outward from the strip. The fins are then folded using a “star wheel”style roller which imparts rounded bends to the fin stock. This approachhas certain disadvantages. For example, the louvered fin arrays do notprovide the maximum heat flux between the fins and the ambient air as aconsequence of air by-pass in the rounded fin areas. In addition, theangled louver designs create unwanted pressure drop differentialsthrough the coil assembly. Also, these fin arrays can be expensive tomanufacture as a consequence of the high tooling costs associated withshear cutting of the fin material.

Alternative approaches to the louvered design have been proposed inorder to overcome some of the problems previously encountered. Forexample, the use of a one-piece elongated serpentine fin array designhas been proposed. The fin array includes top and bottom portionsconnected together by fins extending between adjacent ones of the topand bottom portions. The fins have side edges facing generallyperpendicular to the longitudinal length of the one-piece fin member.The side edges of the completed fins are also offset with respect toeach other in order to improve heat flux with the passing air. Whilethis serpentine fin array design improved heat transfer capabilities, ithas other disadvantages associated with its manufacture.

The one-piece serpentine design can be manufactured by scoring fin stockusing a crush cut method (chisel and anvil). After the fin stock isscored or cut, it is driven through a pair of star wheels. The starwheels bend the fin stock so that the top portion extends in a commontop plane, the bottom portion extends in a common bottom plane, and thefin stock extends between and connects adjacent ones at the top andbottom portions. Because the fin stock is uncompressed, it is placed ina compression device that urges the ends together in order to completemanufacture of the fin array. This manufacturing approach has beenproblematic. For example, the machinery, such as the star wheels, can bevery slow moving, and complicated. More specifically, it has been foundthat the use of star wheels requires that the fin material be folded andgathered with many small angle changes in a multiplicity of staged andsynchronized wheel combinations. This procedure results in an expensivemanufacturing process that is difficult to set up and maintain whilealso being slow moving.

Therefore, there is a need for an improved fin array design that can beeasily and rapidly manufactured while having the same advantageous heattransfer capabilities of the previous serpentine design.

BRIEF SUMMARY

The present invention is directed to an improved fin array and method ofmaking same. More specifically, the present invention is directed to afin array that has significant heat transfer capabilities, such as thosefound in the previous serpentine design, while capable of being easilyand rapidly manufactured.

According to a first aspect of the invention, a fin array is providedhaving a plurality of fins. The fin array is an elongated one pieceelement. The fins include connected staggered top segments and bottomsegments. A top bend axis extends continuously across a plurality of thetop segments.

According to a second aspect of the invention, a fin array is providedhaving a plurality of fins. The fin is an elongated one piece element.The fins include a plurality of connected staggered top segments andbottom segments. Upper and lower bend axes extend continuously through aplurality of the top segments and bottom segments, respectively. Aplurality of staggered fin bend axes extend on both sides of the topbend axis and the bottom bend axis.

According to a third aspect of the invention, a method of forming a finarray is provided. The method includes the step of providing a sheet offin stock. The method also includes the step of positioning and passingthe fin stock through a cutting roller which produces a one-piece finmember including a plurality of fins. The fins include connectedstaggered top segments and bottom segments. The one piece fin member hastop and bottom bend axes extending continuously through the top andbottom segments. The one piece fin member also includes staggered finbend axes on both sides of the top and bottom bend axes. The method alsoincludes the step of bending the fin stock along the top and bottom bendaxes such that the top and bottom segments form a generally flatsurface.

The present invention, together with attendant objects and advantages,will be best understood with reference to the detailed description belowin connection with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a folded fin array in accordance with anembodiment of the present invention;

FIG. 2 is a schematic view of an embodiment of the folding process ofthe fin stock that ultimately forms the fin array shown in FIG. 1;

FIG. 3 is a top plan view illustrating fin stock after having beenpassed through cutting rollers;

FIG. 4 is an enlarged view of forming wheels and fin stock passingoutward therefrom;

FIGS. 5A-H are side views and enlarged portions of the star wheels thatform a portion of the forming wheels; and

FIG. 6 is a perspective view of the fin array after having passedthrough the forming wheels.

DETAILED DESCRIPTION OF THE DRAWINGS AND THE PRESENTLY PREFERREDEMBODIMENTS

The present invention is directed to an improved fin array and heattransfer assembly and method of making same. It will be understood bythose of ordinary skill in the art that the fin array of the presentinvention can be used with a wide variety of heat exchanger assembliesand in various applications. For example, a fin array of the presentinvention could be used in air conditioning condenser coils orautomotive radiators

FIG. 1 illustrates a fin array 10 in accordance with a first embodimentof the present invention. The fin array 10 has a generally serpentinepattern and is preferably formed from a single piece of fin stock.Materials such as aluminum, particularly rolled aluminum fin stock, orcopper or other known materials may be used to form the fin array 10.The fin array 10 includes a plurality of fin sets 14 formed from fins18. The fin sets 14 include top and bottom portions 22, 24. The topportions 22 extend in a common flat top plane and bottom portions 24extend in a common flat bottom plane. The top and bottom portions 22, 24maximize surface contact area with an associated heat exchanger tubethereby maximizing heat transfer between the fins 18 and the associatedheat exchanger tube. In addition, each fin 18 runs continuously fromtube to tube surface giving enhanced heat transfer close to the tubeswhere the temperature differential between fins 18 and air is greatest.

The top and bottom portions 22, 24 are elongated flat sections thatextend generally perpendicular to the running length of the fin array10. The top and bottom portions 22, 24 form a plurality of top andbottom staggered segments 28, 29 generally having a staggered rectangleshape. However, it should be recognized by those of ordinary skill inthe art that other shapes may be implemented.

In the embodiment illustrated in FIG. 1, the fin array 10 includes fourfin sets 14. The fin sets 14 include seventeen fins 18 in theillustrated embodiment. It should again be recognized by those ofordinary skill in the art that more or less than four fin sets 14 may beimplemented and that more or less than seventeen fins 18 may beimplemented. For example, a single fin 18 might be as wide as the finstrip itself or as narrow as 0.002 inches. Fin strips can be of anywidth but are typically in the range of 0.5 inches to 6.0 inches inwidth. The number of fins 18 in each fin set 14 (or repeated pattern) isdefined by the fin pitch (the spacing of fins in the completed foldedfin) and the fin offset (the staggered spacing of fins across the fin).The number of fins 18 in a fin set 14 (pattern repeat) will be notgreater than the fin pitch divided by the fin offset. Fin pitch may varyfrom as little as 0.020 inches to as much as 0.500 inches. Fin offsetmay vary from as little as 0.010 inches to as much as 0.500 inchesdepending on the application. Fin height may also vary greatly from aslittle as 0.100 to as much as 6.0 inches typically.

Each of the fins 18 includes top and bottom edges 30A, 30B. The top andbottom edges 30A, 30B define sides 32A, 32B. The sides 32A, 32Binterconnect the top and bottom portions 22, 24. The fins 18 are offsetfrom one another to provide a gap 38 that maximizes the heat transfer ofthe fins 18 by allowing ambient air ready access to fins 18. The sides32A, 32B extend perpendicular to the longitudinal or abyssal length ofthe fin array 10 in order to further maximize air flow.

The fin array 10 includes a top or ordinential bend axis 40 that extendsacross the top segments 28. In the illustrated embodiment, the top bendaxis 40 extends continuously along the top portion 22. The bottom orordinential bend axis 44 extends along the bottom portion 24 or bottomsegments 29. In the illustrated embodiment, the bottom bend axes 44extend continuously along the bottom portion 24. As explained herein,the use of the term “continuous” is not intended to suggest that theassociated cutting of the fin stock has to be “continuous.” Indeed itcannot be continuous or the fin would fall apart during assemblyoperations. Rather, the cuts are sufficient to cause the material tobend easily and in precise alignment yet remain attached while the bendaxes extend continuously through the material forming the top and bottomportions 22, 24.

FIG. 2 is a schematic view of an embodiment of the manufacturing methodof the present invention 60. The manufacturing process includes using aconventional rotary cutting device (not shown) to cut or score the finstock 62 into the pattern as best shown in FIG. 3. The cut fin stock 62is passed into the folding rollers 68 which fold the cut fin stock 62into the folded fin pattern 70 best illustrated at FIG. 6. The foldedfin pattern 70 is passed into a conventional compression device 72 thatcompresses the ends of the folded fin stock pattern 70 into the finarray 10 illustrated in FIG. 1.

The cut fin stock 62 is best illustrated in FIG. 2. In the preferredembodiment, two cutting rollers and two pinch rollers are provided. Thecutting rollers cut the fin stock into the pattern illustrated in FIG. 2using a conventional crush cut (chisel and anvil) technique. It shouldbe recognized that the cuts forming the bend axes 40, 44 are longer thanthe cuts used to form the fins 18 thereby resulting in an inherentlygreater weakness in the bending of these areas. Two pinch rollers areprovided to assist by flattening out the cut fin stock after eachcutting step. Reference is made to U.S. Pat. No. 6,247,527 issued onJun. 19, 2001 to Roger Paulman, for a further description of the cuttingprocess and other related manufacturing steps, the disclosure of whichis hereby incorporated by reference. It should be noted that other knownmethods of cutting fin stock may be implemented so as to produce the cutfin stock 62.

Referring back to FIG. 2, after the cut fin stock 62 is produced, it ispassed into the folding rollers 68. The folding rollers 68 serve toseparate the fins 18 and fold the fin pattern 70 along the bend axes 40,44. In particular, the folding rollers mechanically force apart the fins18 of the fin sets 14 and bend each fin set at the bend axes 40, 44 asillustrated in FIG. 6. Because the bend axes 40, 44 extend across thetop and bottom portions 22, 24 of each fin set 14, the fin stockmaterial is weakened substantially in order to provide for easy bendingand re-flattening along the associated bend axes. It should be notedthat with some materials the crush cutting technique yields small spursor burrs along the cut edges of the material. These spurs or burrs, whenrun through the flattening rollers, which are a part of this process,often become entangled and consequently must subsequently be forcedapart using mechanical force.

The folding rollers 68 include a plurality of sets of star wheels 90,92, 94, 96. The star wheels 90-96 are formed in sets of four wheels90-96 with four sets shown to form each folding roller in theillustrated embodiment. The star wheels 90, 92, 94, 96 are bestillustrated in FIGS. 5A-H. Each star wheel 90, 92, 94, 96 includesassociated teeth 90A, 92A, 94A, 96A. The teeth 90A, 92A, 94A, 96A arebest illustrated in the enlarged views of FIGS. 5B, 5D, 5F, 5H. Each ofthe teeth 90A, 92A, 94A, 96A is sized differently to produce the offsetpattern of teeth as best seen in FIG. 4. The teeth 90A-96A produce thefins 18 by pressing into the cut fin stock 62. In addition, the topportions 90B-96B and bottom portions 90C-96C are used to bend the finsets 14 along the bend axes 40, 44.

After passing through the folding rollers 68, the folded fin pattern 70is produced. The folded fin pattern 70 includes a plurality of fin sets14 with individual fins 18 formed and partially bent along the bend axes40, 44. A conventional compression device 72 compresses the edges of thefolded fin pattern 70 in order to produce the fin array 10 illustratedin FIG. 1. Because the cuts associated with the bending axis 40 extendacross each fin set 14, the material is weaker in these areas therebyallowing for the folded fin pattern 70 to be readily bent to produce finarray 10. The folded fin pattern 70 is produced by urging it into a boxagainst a backwards force. More specifically, the present inventionovercomes previous problems by positively folding (using opposingwheels) two approximately 90 degree bends (the bottom bend axes 44)along with an approximately third 90 degree bend (the bending axis)which is subsequently flattened back to the straight or nearly straightcondition in the box. This third bend is made such that the fin materialholding the fin together at the bend is much narrower than that of theother bends which are expected to remain at about 90 degrees in thefinal formed fin array. As a consequence of the built-in relative“weakness” the third bend will re-flatten itself back to near flatcondition without changing the two 90 degree bends on either side of itthus resulting in a near perfect “square” final fin configuration.

The embodiments described above and shown herein are illustrative andnot restrictive. The scope of the invention is indicated by the claimsrather than by the foregoing description and attached drawings. Theinvention may be embodied in other specific forms without departing fromthe spirit of the invention. For example, the shape and size of the finsof the fin array may be designed in a manner other than as specificallyillustrated in the figures. Accordingly, these and any other changeswhich come within the scope of the claims are intended to be embracedherein.

It is therefore intended that the foregoing detailed description beregarded as illustrative rather than limiting, and that it be understoodthat it is the following claims, including all equivalents, that areintended to define the spirit and scope of this invention.

1. A fin array for a heat exchanger assembly comprising: an elongatedone piece fin array including a plurality of fins, the fin includingconnected staggered top segments and bottom segments, and a top bendaxis extending continuously across a plurality of the top segments. 2.The fin array of claim 1 wherein a fin material used to form the finmember is cut to generally define the top bend axis.
 3. The fin array ofclaim 2 further comprising a bottom bend axis that extends continuouslyacross a plurality of the bottom segments.
 4. The fin array of claim 3wherein the fin material is cut to generally define the bottom bendaxis.
 5. The fin array of claim 4 further comprising staggered fin bendaxes on both sides of the top bend axis.
 6. The fin array of claim 5further comprising staggered fin bend axes on both sides of the bottombend axis.
 7. The fin array of claim 6 wherein the cuts used to form thetop bend axis and the bottom bend axis are not continuous.
 8. The finarray of claim 7 wherein the staggered segments have a generallyrectangular shape.
 9. The fin array of claim 8 wherein the top andbottom bend axes are weaker than the staggered fin bend axes.
 10. A finarray for a heat exchanger assembly comprising: an elongated one piecefin array including a plurality of fins, the fins including connectedstaggered top segments and bottom segments, and a top bend axis and abottom bend axis that extend continuously through a plurality of the topsegments and bottom segments, respectively, and staggered fin bend axeson both sides of the top bend axis and bottom bend axis.
 11. The finarray of claim 10 wherein the top and bottom bend axes are weaker thanthe staggered fin bend axes.
 12. The fin array of claim 11 wherein thetop and bottom bend axes extend across a width of the fin.
 13. The finarray of claim 12 wherein a group of fins forms a fin set with the topand bottom bend axes extending across each fin set.
 14. The fin array ofclaim 13 wherein the top and bottom bend axes extend straight throughthe top and bottom segments.
 15. A method of making a fin array for aheat exchanger assembly comprising: a) providing a sheet of fin stock;b) positioning and passing the fin stock through a cutting roller whichproduces a one piece fin member including a plurality of fins, the finsincluding connected staggered top segments and bottom segments, and theone piece fin member having the top and bottom bend axes extendingcontinuously through the top and bottom segments, and staggered fin bendaxes on both sides of the top and bottom bend axes; and c) bending thefin stock along the top and bottom bend axes such that the top andbottom segments form a generally flat surface.
 18. The method of claim17 wherein the bend axes are formed by cutting the fin stock.
 19. Themethod of claim 18 wherein the bending of the fin stock requires abending and a re-bending of the fin stock.
 20. The method of claim 19wherein the top and bottom bend axes are weaker than staggered fin bendaxes.